The invention relates to an inspection system for the inspection of defects in sheet material, and more particularly to an inspection system for the inspection of surface and body defects in glass substrates, such as in LCD glass. The inspection system is particularly adapted to accommodating fairly large size substrates in the order of 550 mmxc3x97650 mm and larger, by providing stability to the substrate during inspection through the use of an air support table.
Presently, the inspection of such large size glass panels is primarily done by utilizing manual methods. Accordingly, such manual processes introduce a large amount of variability in the outgoing inspection product. Some of the problems encountered with the known inspection systems include the problem of holding a substrate in a manner which minimizes sheet vibration. In addition there has been problems in holding the glass sheet in a strict plane tolerance so as to have consistency in inspection readings. Further, it has been difficult to provide a direct view of all areas of the sheet without interference from supporting structures. That is, most of the known inspection systems rely on some method of holding the sheet by the edge in either a horizontal or vertical orientation, which creates problems of glass sag and vibration during the inspection process.
It thus has been an object of the present invention to provide a solution to these problems by utilizing a uniform air support for the entire glass surface of a substrate without physically contacting the surface of the sheet, and while dampening any sheet vibrations and allowing the sheet to move at high speeds during inspection.
The present invention sets forth method and apparatus for inspecting surface and body defects in glass substrates. The system includes a dual detector scanning system as well as a brightfield/darkfield imaging system that work together to detect, identify and classify different types of glass defects. The glass is supported in a slightly off-vertical position by an air table during the inspection process to provide stability, particularly for larger size substrates in the order of 550 mmxc3x97650 mm and larger.
Glass sheets or substrates to be inspected are positioned adjacent a three-piece air table which is tilted by an angle from the vertical. The sheets or substrates are indexed substantially vertically, but along an incline or axis parallel to the tilted air table. Dual light delivery mechanisms and dual detectors are positioned adjacent slots formed within the air table on a slide mechanism that allows them to be moved horizontally along an axis transverse to the oblique axis. The glass substrate is positioned over the slots and held stationary while the dual detector and light delivery systems are swept from one edge of the substrate to the other. The glass is then indexed and this process is repeated until the entire area of the glass substrate has been inspected.
Following this initial inspection process, brightfield/darkfield optics can be positioned to review any of the particles or defects detected during the previous scanning process. Scratches, particles and other defects can be identified and accepted or rejected.